Direct Generation of 1030 nm Low-Noise Femtosecond Pulses in All-PM All-Fiber Figure-9 Laser

We report the direct generation of 1030 nm low-noise femtosecond pulses in a phase-biased all-polarization maintaining (PM) all-fiber figure-9 Yb-doped laser. In order to properly balance net-cavity dispersion and nonlinear phase shift to establish soliton mode-locking in figure-9 cavity, we specially designed a 1030 nm chirped fiber Bragg grating with a moderate anomalous dispersion of 0.5 ps2. By precisely controlling the lengths of passive fibers, the net-cavity dispersion of the 1030 nm all-PM all-fiber laser can be managed from negative, near-zero to positive dispersion, and passive mode-locking under the different regimes can be readily initiated. Stable 1030 nm soliton mode-locking operation under a net-cavity dispersion of -0.059 ps2 is achieved to directly generate 890 fs pulses with a spectral bandwidth of 2.85 nm. Interestingly, the phase noise of 1030 nm femtosecond soliton mode-locking in the anomalous-dispersion regime is 20 dB lower than that of dissipative soliton mode-locking in the normal-dispersion regime. Such 1030 nm low-noise soliton fiber laser may be better as light source for fiber femtosecond frequency combs.